diff --git a/hwpfilter/source/grammar.cxx b/hwpfilter/source/grammar.cxx
index d2c91860aeb6..fdcdbb139d75 100644
--- a/hwpfilter/source/grammar.cxx
+++ b/hwpfilter/source/grammar.cxx
@@ -1175,12 +1175,13 @@ yyerrhandle:
   return 1;
 }
 
-
 Node *mainParse(const char *_code)
 {
     initFlex( _code );
     top = nullptr;
     yyparse();
+    deinitFlex();
+
     if( top )
         return top;
     else
diff --git a/hwpfilter/source/lexer.cxx b/hwpfilter/source/lexer.cxx
index 5d0cef7e2f9d..191f0bce7419 100644
--- a/hwpfilter/source/lexer.cxx
+++ b/hwpfilter/source/lexer.cxx
@@ -2107,6 +2107,13 @@ void initFlex(const char *_code )
     yy_switch_to_buffer( yy_scan_string(_code) );
 }
 
+void deinitFlex()
+{
+    // flex faq-memory-leak
+    yy_delete_buffer(YY_CURRENT_BUFFER);
+    yy_init = 1;
+}
+
 int yywrap()
 {
     yy_delete_buffer( YY_CURRENT_BUFFER );
diff --git a/hwpfilter/source/lexer.hxx b/hwpfilter/source/lexer.hxx
index 0f0c1fe1525e..41835f13b51a 100644
--- a/hwpfilter/source/lexer.hxx
+++ b/hwpfilter/source/lexer.hxx
@@ -17,13 +17,11 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  */
 
-#ifndef INCLUDED_HWPFILTER_SOURCE_LEXER_HXX
-#define INCLUDED_HWPFILTER_SOURCE_LEXER_HXX
+#pragma once
 
 void initFlex(char const* s);
+void deinitFlex();
 
 int yylex();
 
-#endif
-
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */